Image sensors are semiconductor devices for converting optical images into electric signals and may be classified generally as a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor.
The CCD image sensor has shortcomings, such as a complicated driving method, high power consumption and a complicated fabricating process requiring a multi-phased photo processes.
As a result of the afore-noted shortcomings in the CCD image sensors, CMOS image sensors are thought to be the next generation image sensor. CMOS image sensors may include a photodiode region for receiving a light signal and converting the received light signal to an electric signal and a transistor region for processing the electric signal. In this regard, the CMOS image sensor may include a photodiode and a MOS transistor in a unit pixel. The CMOS image sensor may generate an image by sequentially detecting electric signals in a switching mode using the photodiode and the MOS transistor.
The photodiodes in a CMOS image sensor may be horizontally disposed with transistors. Particularly, the photodiodes and the transistors are provided horizontally adjacent to each other on and/or over a semiconductor substrate. Therefore, additional space or surface area is required for the photodiode. The requirement of additional space or surface area may be undesirable as reducing a fill factor region and limiting the possibility of resolution. Moreover, it may be difficult to optimize a process for simultaneously forming photodiodes and transistors on and/or over a semiconductor substrate.
In order to overcome such shortcomings, a method for vertically integrating transistor circuitry and a photodiode was introduced.
Example FIG. 1 illustrates a vertical integration type image sensor that may include substrate 110, first line 130 formed on and/or over substrate 110, intrinsic layer 150 formed on and/or over first line 130, second conductive layer 160 formed on and/or over intrinsic layer 150, and second line 170 formed on and/or over substrate 110. Here, a COM circuitry (not shown) having a lower line 120 may be formed on and/or over substrate 110. First conductive layer 140 may be formed between first line 130 and intrinsic layer 150.
First line 130 may be composed of various conductive materials such as metal, alloy, and silicide. For example, first line 130 may be composed of aluminum, copper, and cobalt. First line 130 may be patterned by a photodiode unit pixel or by a photodiode unit pixel after first conductive layer 140 is formed on and/or over first line 130.
First conductive layer 140 may be selectively formed and serve to operate as an N-layer of a PIN diode. Particularly, first conductive layer 140 may be composed as an N-type conductive layer formed by N-doped amorphous silicon. First conductive layer 140 may be composed of a-Si:H, a-SiGe:H, a-SiC, a-SiN:H, and a-SiO:H by adding germanium, carbon, nitride, or oxygen to amorphous silicon.
Intrinsic layer 150 may serve to operate as an I-layer of a PIN diode. N-doped amorphous silicon may be used to form intrinsic layer 150. Second conductive layer 160 may serve to operate as a P-layer of a PIN diode, particularly, as a p-type conductive layer. Second conductive layer 160 may be composed of P-doped amorphous silicon. Second line 170 may serve to operate as an upper electrode of a photodiode and be electrically connected to the exposed lower line 120a. Second line 170 may also be formed as a transparent electrode having high light transmissivity and high conductivity. Second line 170 may be composed of indium tin oxide (ITO) or cardium tin oxide (CTO).
Such a vertical integration type image sensor has numerous shortcomings. For instance, second line 170 operates as an upper electrode of a photodiode, and thus, is a core element of the vertical integration image sensor. Because second line 170 may be composed of a metal material such as ITO, it can be easily broken or peeled off due to a lack of flexibility. This will significantly reduce the quality and a reliability of a product using such a vertical integration type image sensor.